Biotic factors are the effects of living organisms on a population. In AQA terms, population size can vary as a result of interactions between organisms: competition and predation. Disease and parasitism also act as biotic factors.The main biotic factors are:• Intraspecific competition: competition between individuals of the same species for resources such as food, water, light, space and mates.
• Interspecific competition: competition between individuals of different species for the same resources.
• Predation: one organism (the predator) kills and eats another (the prey), so the size of each population affects the other.
• Disease and parasites: pathogens and parasites reduce the survival and reproduction of their hosts and spread more easily when populations are dense.Many biotic factors are density dependent: their effect gets stronger as the population becomes larger and more crowded. For example, the more individuals there are, the fiercer the competition for food and the faster a disease spreads. This is one reason populations tend to level off at the carrying capacity instead of growing for ever.Biotic and abiotic factors interact. A cold winter (abiotic) may reduce the food supply, which increases competition (biotic), and weakened animals are more likely to be caught by predators or to become infected.Each of the main biotic interactions is explored in its own lesson.
• Interspecific competition: competition between individuals of different species for the same resources.
• Predation: one organism (the predator) kills and eats another (the prey), so the size of each population affects the other.
• Disease and parasites: pathogens and parasites reduce the survival and reproduction of their hosts and spread more easily when populations are dense.Many biotic factors are density dependent: their effect gets stronger as the population becomes larger and more crowded. For example, the more individuals there are, the fiercer the competition for food and the faster a disease spreads. This is one reason populations tend to level off at the carrying capacity instead of growing for ever.Biotic and abiotic factors interact. A cold winter (abiotic) may reduce the food supply, which increases competition (biotic), and weakened animals are more likely to be caught by predators or to become infected.Each of the main biotic interactions is explored in its own lesson.